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Well log and seismic character of tertiary terumbu carbonate, South China Sea, Indonesia
Abstract
The Esso Exploration and Production Inc. Natuna D-Alpha block lies approximately 125 mi (200 km) northeast of Natuna Island in the Indonesian portion of the South China Sea. The block contains a large Miocene platform carbonate complex called the L-structure. The Terumbu Formation L-structure, situated in front of and isolated from a much larger carbonate shelf, is similar to the carbonate atolls developed in front of the barrier-reef complex offshore of Belize. The lower platform and upper platform have a similar log character. The detrital facies is composed of fore-reef talus, pelagic, and hemipelagic carbonates. By mapping the Terumbu carbonate facies, the growth history of the L-structure is revealed.
... Some such surfaces have reddish coloration suggestive of either subaerial or submarine exposure, but no conclusive sedimentologic evidence of emergence has yet been found in the Leg 194 cores. Subaerial exposure is, however, widely reported in other southwest Pacific Miocene carbonate platforms and is believed to be of great importance for improving reservoir quality (Epting 1980(Epting , 1989McArthur and Helm 1982;Wright and Hardian 1982;Mundt 1983;May and Eyles 1985;Grange and Davies 1985;Leamon and Parsons 1986;Longman et al. 1987;Mayall and Cox 1988;Dolan and Hermany 1988;Rudolph and Lehmann 1989;Gibson-Robinson et al. 1990;Jordan and Abdullah 1992;Sun and Esteban 1994;Moldovanyi et al. 1995;Park et al. 1995;Mayall et al. 1997;Grö tsch and Mercadier 1999;Wilson and Evans 2002;Kusumastuti et al. 2002;Fournier et al. 2004;Vahrenkamp et al. 2004;Neuhaus et al. 2004;Heubeck et al. 2004;Bachtel et al. 2004). ...
... Many local examples, summarized in the stratigraphic correlation panels of Wilson (2002), seem to support this general pattern, at least in showing prolific carbonate platforms existing in early to middle Miocene time and lesser or no late Miocene carbonates in the same areas. Specific examples include the lower-upper Miocene Belumai Formation of the North Sumatra Basin, offshore northeast Sumatra (McArthur and Helm 1982;Mundt 1983); the lower Miocene Arun Limestone, onshore north Sumatra (Jordan and Abdullah 1992); the lower-upper Miocene Darai Limestone of the Papuan Basin, Gulf of Papua (Leamon and Parsons 1986); the lower-upper Miocene Kais Formation, onshore western Irian Jaya (Vincelette and Soeparjadi 1976;Dolan and Hermany 1988;Gibson-Robinson and Soedirdja 1986;Gibson-Robinson et al. 1990); lowerupper Miocene Luconia carbonate buildups, Sarawak Basin, offshore northwest Borneo (Doust 1981;Epting 1989;Zampetti et al. 2004;Bracco Gartner et al. 2004;Vahrenkamp et al. 2004); the Chattian-Burdigalian Gomantong Limestone of eastern onshore Borneo (Noad 2001); the middle-upper Miocene Natuna Platform, Sarawak Basin, offshore northwest Borneo (May and Eyles 1985;Rudolph and Lehmann 1989); the middle Miocene-lower Pliocene Segitiga Platform, offshore northwest Borneo (Bachtel et al. 2004); the early Miocene Zhujiang Formation of Liuhua Field, Pearl River Mouth Basin, offshore China (Erlich et al. 1990;Erlich et al. 1993;Tyrrell and Christian 1992;Moldovanyi et al. 1995;Heubeck et al. 2004); lower to upper Miocene carbonates of the Nam Con Son Basin, offshore Vietnam (Matthews et al. 1997); middleupper Miocene carbonates of the Visayas area, onshore central Philippines (Carozzi et al. 1976); the Eocene-middle Miocene Tonasa Formation, onshore southwest Sulawesi (Wilson and Bosence 1997;Wilson 1999;Wilson et al. 2000;Wilson 2000); the Eocene-middle Miocene Tende Hantu, Taballar, and Domaring formations, Mangkalihat Peninsula, onshore eastern Borneo (Wilson and Evans 2002); lowermiddle Miocene Mahakam Delta patch reefs, onshore eastern Borneo (Wilson and Lokier 2002), the lower-middle Miocene Wonosari carbonate platform, onshore south Java (Wilson and Lokier 2002); the lower-upper Miocene Gunung Putih carbonate complex, offshore northeast Java (Cucci and Clark 1993); and the Chattian-lower Miocene Prupuh Formation, Madura Strait, offshore and onshore northeast Java (Kusumastuti et al. 2002). ...
Strontium-isotope stratigraphy has been used to examine the timing of depositional events and dolomitization in two Miocene carbonate platforms cored by Ocean Drilling Program (ODP) Leg 194, just seaward of the Great Barrier Reef. The results provide firm constraints for correlating surfaces and depositional stages between the two platforms and thereby relating seismic sequences previously defined in the off-platform sediments to the lithostratigraphic units described from cores in the seismically transparent platform-top sites. Oyster-bearing beds at the base of both platform successions yield early Oligocene ages (29-31 Ma), thus dating initial transgression of the Marion Plateau's volcanic basement. There followed a period of slow accumulation of shallow-water grainstones rich in quartz and phosphate grains in late Oligocene time (2923 Ma; seismic Megasequence A). The main growth of the carbonate platforms took place in early to late Miocene time (237 Ma), comprising five depositional sequences. The first four of these (seismic Megasequence B) are common to both platforms and terminated with a possible karst surface at 10.7 Ma. Different sedimentologic expression of this megasequence in the two platforms reflects contrasting progradational versus aggradational geometries in the locations studied. The final growth stage (seismic Megasequence C) occurred only in the southern platform and terminated at 6.9 Ma. Both platform-demise events (10.7 and 6.9 Ma) approximately coincide with falls in global sea level combined with longer-term trends of decreasing water temperature. Sr-isotope ages of dolostones; increase with depositional age, and older dolostones in the southern platform have more coarsely crystalline and fabric-destructive textures than overlying younger dolostones. These relationships are consistent with dolomitization by normal seawater shortly after deposition and overprinting of multiple times of dolomite recrystallization and cementation in the deeper strata.
... The seismic identification of organic RCPs is determined according to its internal reflection structure, external geometry and contact relationship with the surrounding rocks [25][26][27][28]. In this paper, organic reefs are classified according to their development position and growth morphology. ...
In this study, high-resolution seismic profiles and well data provided a good opportunity for better understanding the reefs and carbonate platforms in the Wan’an Basin, southwest of the South China Sea, and also provided valuable information for the oil–gas exploration in the reef reservoirs. Four evolutional phases, including the initial phase, the prosperous phase, the recession phase and the submerged phase, of the reefs and carbonate platforms are proposed according to our data. In the Early Miocene, a few small, isolated carbonate platforms initiated in the center of the basin. In the Middle Miocene, they flourished and mainly formed around the Northern Uplift and Central Uplift, with two belts of carbonate platforms in the western area and eastern area that were mainly platform-edge reefs, massive reefs and a few point reefs. In the Late Miocene, the carbonate platforms began to retreat towards the high topographic position because of the rising of sea level. Meanwhile, the numbers and styles of reefs increased to include platform-edge reefs, massive reefs, atoll reefs and point reefs. Since the Pliocene, most of the carbonate platforms have been covered by detrital materials from terrestrial sources. Crustal tectonic activity provides favorable topography for reef growth and the distribution of platforms, and eustasy controlled the vertical growth and lateral migration of reefs. Since the Late Miocene, the rapidly crustal tectonic subsidence and the rising of relative sea level may lead to the drowning of the carbonate platform.
... The largest oilfi eld in the South China Sea is the Liuhua 11-1 oilfi eld in the vast organic reef area of the Pearl River Mouth Basin, and the largest gas fi eld lies in Organic Reef L of the Zengmu Basin. The reservoirs of the two fi elds belong to the bioherm dolomites formed in the Miocene (May and Eyles, 1985;Lü et al., 2002), which is consistent with the well intervals in the present study. Comparison of results from worldwide petroleum exploration suggests that many reservoirs are composed of dolomites. ...
Carbonate rocks are important reservoirs for global petroleum exploration. The largest oilfield in the South China Sea, Liuhua 11-1, is distributed in the massive carbonate reef area of the Zhujiang (Pearl) River Mouth Basin. Previous studies showed that one 802.17-m-long core from well Xichen-1 in the South China Sea mainly consisted of white and light gray-white organic reefs. Recently, a Miocene whole core (161.9 m long) of well Xiyong-2, near well Xichen-1, was found to contain six layers of yellowish brown, light yellowish gray, iron black, or light yellowish gray-white organic reefs. Scanning electron microscope images of these layers reveal a typical ferroan dolomite rich in Fe (up to 29%), with the high concentrations of Mn, Cu, W, Zn, Cr, Ni, and Co. Systematic X-ray powder diffraction analysis yields a 1.9–6.1 match in phase ratio with ankerite, 5.4–26.9 with dolomite, and zero with calcite, which indicate that the samples can be classified as ferroan dolomite. The iron and heavy metals are inferred to be originated from multiple volcanic eruptions of Gaojianshi Island in the Dongdao Atoll during the middle-late Miocene. These elements were dissolved in seawater, likely as a sol, and carried to Yongxing Island in the Xuande Atoll by sea currents and tides enhanced by prevailing winds, and deposited as a part of the sedimentation process in the study area. The ferroan dolomite has Sr content of (125–285)×10⁻⁶, which is lower than the accepted Sr boundary value of dolomite. This finding suggests that dolomitization occurred during large-scale global glacial regression in the late Miocene. The isolated Xisha carbonate platform, exposed to air, underwent freshwater leaching and dolomitization induced by mixed water, and caused the extensive Fe-Mg exchange along the organic reef profile to form ankerite and ferroan dolomite. These results may help to understand paleoceanographic environmental changes in the South China Sea during the Miocene.
... Well AP-IX, drilled on the Terumbu shelf margin 25 km west of the Natuna Platform, penetrated Cretaceous granodiorites below the Arang Formation. A similar Cretaceous granitic basement cropped out on Borneo and Natuna Islands (Hamilton, 1979;May and Eyles, 1985). From the geochronological analysis and the normal faulting of the basement, the rifting event likely occurred during the Late Oligocene to Early Miocene. ...
Widespread and tremendously thick Cenozoic carbonate sequences are present along the margins of the South China Sea (SCS). However, most of the sequences have been drowned since the Late Miocene. The stratigraphic architecture of the carbonate platforms in the SCS can provide information on the tectonic evolution of the ocean basin. Based on 2D/3D seismic, well and regional geologic data, we have interpreted the Cenozoic SCS carbonate platforms along the continental margins. The carbonate platforms developed during rifting and initiated on the fault block of the conjugate rifted margins. Most of the carbonate platforms became drowned after the Middle Miocene. The Malampaya Carbonate Sequences, which have thicknesses of greater than 600 m, developed on a horst of an Oligocene rifted block. Tectonic subsidence provided accommodation for the growth of the carbonate platforms. Tectonic tilting, faulting, and the foreland bulge controlled the distributions, thicknesses, and horizontal seismic reflection variations of the drowned carbonate platforms. The tectonic evolution and relative sea-level fluctuations controlled the depositional cycles of the carbonate platforms. We quantitatively calculated the factors that affected the extension and subsidence rates using balanced cross section and backstepping techniques. Our results have demonstrated that the carbonate platforms flourished during the Middle Miocene due to stable tectonic conditions and shrank during the Late Miocene due to rapid subsidence. The relative sea level exerted a second-order control on the evolutionary trend of the carbonate platforms and a third-order control on the evolutionary periods in each stage.
... The late Oligocene to Miocene was a period of widespread carbonate deposition in southeast Asia (Epting, 1980;Fulthorpe and Schlanger, 1989;Ehrlich et al., 1993;Saller et al., 1993;Gucci and Clark, 1993;Sun and Esteban, 1994). Many of these late Tertiary carbonate sequences have been targets of hydrocarbon exploration and numerous oil and gas reservoirs being discovered [i.e., Malaysia: Central Luconia (Ho, 1978;Epting, 1980;Epting, 1989;Sulaiman, 1995); Philippines: Nido (Withjack, 1985) and Malampaya (Grötsch and Mercadier, 1999); Indonesia: Arun (Abdullah and Jordan, 1987;Jordan and Abdullah, 1992), northwest Java Sea (Yaman et al., 1991); Ramba (Longman et al., 1987); South Lho Sukon (Maliki and Soenarawi, 1991), Natuna (May and Eyles, 1985;Rudolph and Lehmann, 1989); China: Liuhua, Pearl River (Moldovanje et al., 1995)]. ...
The Mega Platform is a 30- � 50-km-large and 1.2-km-thick middle Miocene
carbonate platform located in the Luconia Province, offshore Sarawak, Borneo.
The platform originated in the late early to early middle Miocene on a regional
fault-bounded structural high, first aggraded and then backstepped during a series of
third-order sea level fluctuations during the middle Miocene (TB2.3–2.6).
The Jintan Platform termination with an area of 8 � 12 km is one of the prominent
backsteps toward the top of the Mega Platform. Three-dimensional (3-D) seismic indicates
that growth on Jintan ceased relatively early with continued carbonate aggradation
in adjacent smaller terminations (M1, M1-East). Spectacular reservoir architecture
and diagenesis are revealed by the seismic. Several transgressive, aggradational, and progradational
cycles are overprinted by repeated karst events. Dissolution features and bank-margin collapse are aligned to a deep-seated regional fault system, which periodically
became reactivated during carbonate growth. A large triangular-shaped graben
formed during one of the faulting periods but subsequently healed by a prograding reefmargin
sequences.
Two alternative scenarios are presented to explain the ultimate demise of the platform.
The first proposes drowning resulting from a combination of subsidence and eustatic
sea level rise. The second evokes a much-later drowning, which was preceded by a
long period of exposure resulting froma second-order sea level fall and an initial decrease
in subsidence caused by the onset of tectonismin Borneo during the late Miocene. In any
case, following a hiatus of about 5 m.y., the platform was finally buried by deep-marine
siliciclastics that prograded into the basin from the large delta systems of northwest
Borneo.
Recognition of growth architecture, faulting, and karstification is a key to exploiting
the hydrocarbon reservoirs of the Mega Platform. A 30-m-thick low-porosity and
-permeability layer shields the gas trapped in Jintan from the underlying aquifer.
Penetrated by only one well, the extent of the layer and areas of breaching caused by
faulting and karstification are identified on seismic. Interpretation of the seismic is
critical to assessing whether and how the underlying aquifer is felt during reservoir
depletion and whether there is pressure communication between adjacent reservoirs
connected via the aquifer. Cores and logs from three wells provide ground truthing of
reservoir architecture, karst features, and faulting derived from the interpretation of
reflection and inversion seismic. The interpretation is then imported into static and
dynamic 3-D models to constrain reservoir properties, predict dynamic behavior, and
guide optimum field development.
... Many of these Late Tertiary carbonate sequences have been the target of hydrocarbon exploration with numerous gas and oil reservoirs being discovered [i.e. Malaysia: Central Luconia (Epting, 1980, 1989; Philippines: Nido (Withjack, 1985) and Malampaya (Shell Philippines); Indonesia: Arun (Abdullah and Jordan, 1987;Jordan and Abdullah, 1992), NW Java Sea (Yaman et al., 1991); Ramba (Longman et al., 1987); South Lho Sukon (Maliki and Soenawari, 1991), Natuna (May and Eyles, 1985;Rudolph and Lehman, 1989); China: Liuhua, Pearl River (Moldovanje et al., 1995)]. ...
... By late Oligocene time, the center of carbonate growth shifted to area now called the Reed Bank (Liyue) and further north (Taylor and Hayes 1980). In the Zengmu Basin (East Natuna), a distinct middle to late Miocene carbonate complex called the Terumbu Formation L-structure is mainly composed of boundstones, grainstones and packstones that have been homogenized by organic activity (May and Eyles 1985). During the late Miocene, carbonate platforms were widely developed also in the southeastern Wan'an (Nam Con Son) Basin not affected by the Mekong Delta ( Fig. 3.1; Fig. 3.5) (Matthews et al. 1997), as well as offshore Sabah (Madon and Redzuan 1999b;. ...
Over the last three decades, intensive industrial drilling and marine geological research climaxing with ODP Leg 184 have generated voluminous data on the variations and distribution of sediment sequences in the South China Sea (SCS). Lithostratigraphy, biostratigraphy and sequence stratigraphy provide evidence of regional tectonic activities and basin evolution. In addition to these classical approaches toward stratigraphic correlation, isotopic stratigraphy based on tuned astronomical cycles is playing an increasingly important role in refining the regional stratigraphy, especially at deep-sea settings. ODP Site 1148 is unique worldwide in providing a continuous isotope sequence for the last 23 myr, and ODP Site 1143 represents one of the best ODP sites worldwide with the highest time-resolution isotope record for the last 5myr.
... Pk Terumbu Formation, Natuna, S. China Sea May & Eyles (1985), Rudolph & Lehmann (1989), Bachtel et al. ...
This study reviews how shallow water carbonates are revealing environmental and climatic changes on all scales through the last 50 million years in SE Asia. Marine biodiversity reaches a global maximum in the region, yet the environmental conditions are at odds with the traditional view of 'blue-water' reefal development. The region is characterized by complex tectonics, major volcanism, high terrestrial runoff, nutrient influx, everwet and monsoonal climates, low salinities, major currents and ENSO (El Niño Southern Oscillation) fluctuations. Terrestrial runoff, nutrient upwelling, tectonics, volcanism and recent human activities are major influences on the modern development of carbonate systems. Coral sclerochronology is revealing how these factors vary locally over annual and decadal scales. The strong impact of vertical tectonic movements and the interplay with eustasy is evaluated from Quaternary and Pleistocene coral reef terraces. Isotopic data from terrace deposits indicates that interglacials may have been up to 3-6 °C warmer than glacials, consistent with the region's record from terrestrial and deep marine deposits. Study of outcrop and subsurface carbonate deposits reveals the impact of tectonics, siliciclastic, nutrient influx, eustasy and oceanography on individual systems over millennial timescales. Major changes in oceanography, plate tectonics, climate change and perhaps fluctuating CO 2 levels impacted Cenozoic regional carbonate development. Results of studies from terrestrial and deep marine realms are comparable with those from the carbonates, but have yielded higher resolution records of changing currents, precipitation and the monsoons. There is considerable scope for further research, however, SE Asian carbonates are powerful tools in evaluating past environmental change in the equatorial tropics.
... Many carbonate platforms are dolomitized in the upper part of their succession with a dolomitization 'front' descending down from the sequence boundary/unconformity at the top of the platform. This is the case with the Upper Permian (Zechstein) Raisby Formation of NE England (Tucker, 1991), the Triassic Lower Muschelkalk of Catalonia, Spain (Calvet et al., 1990) and both the lower and upper platform sequences of the Miocene Terumbu carbonates in the East Natuna Basin (May and Eyles, 1985). In some cases, such as the Lower Ordovician Ellenburger Formation of Texas for example (Kupecz and Land, 1994), the upper part of a platform has been subjected to karstification, and there is then the problem of whether the dolomitization took place before or after the subaerial exposure. ...
Increased seawater circulation within a carbonate platform, generated through transgression and flooding of the platform, is proposed here as a cause of the common selective dolomitization of calcitic silts in the upper part of limestone sequences of the Barremian-Aptian Urgonian platform of SE France, which underwent selective porosity creation as a result of karstification during an Aptian relative sea-level fall. Parts of this porosity are infilled by microcrystalline dolomite, and some of the host limestone is partially to completely dolomitized. The microcrystalline dolomite is considered to have formed by dolomitization of calcitic silt internal sediment within the karstic cavities as a result of the pumping of seawater through the upper layers of the platform during subsequent transgression. The calcitic silt provided abundant nucleation sites for the dolomitization. Seawater dolomitization following subaerial exposure of limestone is likely to be a common phenomenon if there is sufficient meteoric diagenesis and porosity production and a prolonged period of submarine erosion, winnowing and condensed sequence formation, enhancing the amount of circulation of seawater as seafloor sediment is lithified.
... One large, as yet non-productive gas field, ''D-Alpha'' is present in a large carbonate buildup in eastern Natuna (May and Eyles, 1985). The gas contains a high percentage of CO 2 , suggesting that the charge is derived from deepseated sources associated with crustal faults along the western margin of the South China Sea. ...
Indonesia contains many Tertiary basins, several of which have proven to be very prolific producers of oil and gas. The geology and petroleum systems of these productive basins are reviewed, summarized and updated according to the most recent developments. We have linked the recognized petroleum systems to common stages in the geological evolution of these synrift to postrift basins and classified them accordingly. We recognize four Petroleum System Types (PSTs) corresponding to the four main stages of geodynamic basin development, and developed variably in the different basins depending on their depositional environment history: (i) an oil-prone Early Synrift Lacustrine PST, found in the Eocene to Oligocene deeper parts of the synrift grabens, (ii) an oil and gas-prone Late Synrift Transgressive Deltaic PST, located in the shallower Oligocene to early Miocene portions of the synrift grabens, (iii) a gas-prone Early Postrift Marine PST, characteristic of the overlying early Miocene transgressive period, and (iv) an oil and gas-prone Late Postrift Regressive Deltaic PST, forming the shallowest late Tertiary basin fills. We have ascribed the petroleum systems in each of the basins to one of these types, recognizing that considerable mixing of the predominantly lacustrine to terrestrial charge has taken place. Furthermore, we have grouped the basins according to their predominant PSTs and identified “basin families” that share important aspects of their hydrocarbon habitat: these have been termed proximal, intermediate, distal, Borneo and eastern Indonesian, according to their palaeogeographic relationship to the Sunda craton of Southeast Asia.
... Carbonate sedimentation therefore occurred in a range of marine settings, where conditions were suitable, over large parts of eastern Borneo (Fig. 1), the Makassar Straits, the east Java Sea and western Sulawesi. May and Eyles, 1985;Rudolph and Lehmann, 1989;Dunn et al., 1996 Luconia ( Larger benthic foraminifera dominate Adams and Haak, 1962;Adams, 1965;Abdullah and Yaw, 1993 Keramit ( Marls and breccias Planktonic foraminifera and larger benthic foraminifera Adams, 1965 Bukit Sarang Limestone (S) Sarawak Oligocene (Tc) ...
Modern and Tertiary carbonate production is, and was, extensive and diverse in the seas surrounding Borneo, and mirrors the variety of carbonate depositional systems seen in SE Asia. The availability of favourable conditions for carbonate sedimentation around Borneo was related to a combination of factors, including tectonic setting, the formation of large basinal areas, differential subsidence providing shallow marine areas, a tropical climate and a range of local factors, such as currents or limited clastic input. A detailed sedimentological and diagenetic study was undertaken of middle Eocene to Plio–Pleistocene carbonates which developed in the north Kutai Basin and the Mangkalihat Peninsula, northeast Kalimantan. Carbonate sedimentation in this area occurred in a range of depositional environments, from mixed carbonate clastic shelves, localised and transient shoals or reefs, a variety of platform top settings to deep water redeposited carbonates. An understanding of carbonate depositional environments, spatial facies relationships, and diagenesis is essential in order to develop models for these carbonates which can be used as predictive tools in the subsurface. This study also helps to evaluate tropical carbonate development in SE Asia and the evolution of sedimentary environments in Borneo during the Cenozoic.
... The possible reef inFigure 14 lies just west of an abrupt downward thickening of the basin fill, which probably reveals the location of an old basin margin. These reflection characteristics are similar to characteristics reported from studies of buried reefs (Bubb and Hatelid, 1978; May and Eyles, 1985; Fontaine et al., 1987; Middleton, 1987; Davis and Jackson, 1988; Anderson et al., 1988 Anderson et al., , 1989Erlichetal., 1990; Johnson, 1991; Johnson and Pflueger, 1991; Biddle et al., 1992). If any of the seismically defined reef masses from the North Aoba Basin are in place, they indicate considerable (0.5 to 2 km) submergence of the island arc. ...
Drilling at Sites 832 and 833 in the intra-arc North Aoba Basin sampled an uppermost Miocene but primarily Pliocene and younger section. Many of the lithostratigraphic units identified correlate with events in seismic reflection data. Although the complex geology within this basin makes it difficult to extend detailed stratigraphy far from the drill sites, general aspects of the onshore and offshore stratigraphy are similar. For example, Pliocene carbonate-rich and relatively volcanic-poor rocks on Espiritu Santo Island are exposed on Maewo Island and were penetrated at both sites. These rocks produce a highly diverse reflection signature, which varies from poor reflections to high-amplitude parallel reflections. A major angular unconformity evident in seismic reflection data was one of the main targets of drilling; the unconformity dates from the early Pleistocene. Pleistocene volcanic sediment sampled in the shallowest part of the holes correlates temporally with volcanism along the active volcanic arc. Some of the strong reflections from these rocks stem from interbedded carbonate-rich and volcanic-rich layers. Reefs evident in offshore rocks indicate long-term submergence of the area east of Espiritu Santo Island. Seismic data show that below the deepest drilled rocks at Site 832 the basin fill includes primarily a channeled-fan complex that thins markedly into the basin and was probably derived during late Miocene erosion of Espiritu Santo Island.
... Thus we can contrast the middle to late Miocene Natuna platform (South China Sea, average subsidence rate 0.11 m/ky; Rudolph and Lehmann 1989) with the Oligocene to early Miocene Malampaya platform (offshore Philippines, average subsidence rate 0.05 m/ky; Grötsch and Mercadier 1999). Qualitative observations indicate that Natuna has minimal early meteoric products, with ''leached'' porosity formed late, through burial processes (May and Eyles 1985), whereas Malampaya has undergone significant early meteoric ''leaching'' and cementation (Grö tsch and Mercadier 1999). Our simulations suggest that we might expect still more diagenetic overprinting in Tertiary carbonates of the Caribbean where the passive-margin setting is reflected in lower subsidence rates (, 0.025 m/ky; McNeill et al. 2001). ...
Icehouse carbonate diagenesis is complex, with carbonate sequences being exposed to multiple meteoric hydrozones (vadose-zone, freshwater-lens, mixing-zone) on multiple occasions. A forward modeling approach using CARB3D(+) has enabled quantitative exploration of the nature of this diagenetic overprinting, by explicit simulation of meteoric hydrozone residence times during evolution of an isolated carbonate platform. A sensitivity analysis was performed, encompassing the fundamental controls on hydrozone residence time; frequency and magnitude of sea-level variation, subsidence rate, and climate, the latter via its effect on freshwater-lens thickness and rate of dissolutional lowering of the land surface. Residence time within all meteoric hydrozones is characterized by a high degree of lateral continuity. Vertical continuity is much more limited, with significant variations on a fourth order sequence scale across the platform. Below sequence boundaries prolonged exposure to the vadose zone results from multiple missed beats (when the platform remains exposed at relative sealevel maxima). Overprinting gives total meteoric residence times significantly in excess of the duration of exposure of the overlying sequence boundary. There is a hierarchy of eustatically driven overprint cycles, with higher-frequency cyclicity modifying the primary signal generated by lower-frequency cycles. Fifth-order cycles thus have only a minor impact on hydro one residence times, whilst third order (seismic scale) cycles are a critical control, and could be used as a first-order approximation of the amount of diagenetic overprinting. Subsidence has a strong control on residence time, with greater overprinting at lower subsidence rates, but in high-subsidence regimes sediment packages move below the zone of meteoric-water influence sufficiently rapidly that residence time can be minimal. High land-surface dissolution rates, which result from a wetter climate, remove a large proportion of the subaerially exposed sediment and reduce vadose-zone residence time. Higher effective recharge can increase the thickness of freshwater lens and mixing zones which increases residence times significantly. Residence times in the vadose zone can be directly linked to a sequence stratigraphic framework, but for the freshwater lens and the mixing zone this is possible only with a well constrained relative sea-level history.
... Laterally, this sandstone content decreases from >40% in the west to < 10% in the east. These sediments are underlain by Upper to Middle Miocene carbonates deposited in platform and reef environments, and in turn by Lower Miocene to Oligocene sandstones, shales and thin coal beds laid down in fluvial, lacustrine, deltaic and littoral environments [25][26][27][28][29][30]. ...
A quantitative model is proposed to estimate the magnitude of eustatic sea level fluctuations on the basis of definitions of relative and eustatic sea level. In this model, factors such as erosion, sedimentation, compaction, basement tectonic and loading subsidence, and paleo-bathymetry are considered. To estimate incremental changes in eustatic sea level, we developed methods to solve for the variables involved in the model on the basis of interpretation of seismic profiles. We reconstructed the onlap/offlap points removed by erosion by fitting the effective thickness in areas without erosion with a piecewise-defined function and extrapolating this function to zero thickness. We used decompaction and backstripping algorithms to remove the effect of compaction and to calculate loading subsidence of the basement. Regional data, however, are needed to estimate the paleo-water depths and the tectonic subsidence. For this reason, our methodology is considered semi-qualitative. As an application of this model, an eustatic sea level curve since the Pliocene (5.33 my) was deduced from interpretation of our high-resolution seismic data from the northern Sunda Shelf, South China Sea (SCS). On this curve, 36 fourth order sea level cycles were recognized with periods ranging from 0.08 to 0.29 my. The curve matches well with the smoothed deep-sea stable oxygen isotope curves from benthic foraminifera.
... In and Eyles, 1985;Rudolph and Lehmann, 1989), and approximately ~3.8 Ma (Early Pliocene time) in Segitiga Platform ( Bachtel et al., 2004). ...
Numerous isolated carbonate platforms developed in the Central Luconia Province of offshore Sarawak (during Middle to Late Miocene time). Fault-bounded highs produced largely by extensional deformation and later overprinted by strike-slip deformation provided substrates for the platforms and affected their growth histories. Flooding of these structural highs at ~16.5 Ma initiated carbonate sedimentation nearly simultaneously across the area. Later, third-order sea-level fluctuations and extrinsic factors such as differential subsidence, paleowind patterns and siliciclastic influx then controlled the internal architecture of the platforms. 2-D regional seismic lines, publicdomain data and published literature were used to analyze growth patterns and demise of carbonate platforms across the study area. Five Growth Stages were recognized in the carbonate platforms based on seismic facies analysis and stratigraphic relationships between reflectors. Platforms from the southeastern part of Central Luconia are thicker and larger than platforms located toward the central and northwestern areas, which reflect greater long-term tectonic subsidence to the southeast. Additionally, northwestward prograding siliciclastic sediments from mainland Borneo caused additional flexural subsidence in the eastern part of the area and environmental deterioration for platforms located beyond the range of active siliciclastic sedimentation. Both of these factors reduced the growth potential of platforms and thus subdued carbonate development. Platform termination was regionally diachronous and was produced in two steps. The first platforms drowned (~12.5-9.7 Ma) were in the eastern parts of the study area which were affected by incoming siliciclastic sediments and high local subsidence. Platforms drowned later (~6.3-5.5 Ma) were caused by a rapid sea-level rise combined with an intense local subsidence. Carbonate accumulation rates were measured between intraplatform markers, resulting in a trend that indicates a decrease in sedimentation rate with the square root of time. Comparisons between Central Luconia carbonates and age-equivalent carbonate platforms elsewhere in East Natuna Basin showed that Central Luconia carbonate platforms were drowned earlier (latest late Miocene time) than East Natuna carbonate platforms (Early Pliocene time).
Biogenetic reefs of well Xichen 1, Xisha sea area are mainly plant reefs which consist of calcareous alga, including Rhodophyta shell-like coralline algae, articulated coralline algae and Chlorophyta Halimeda, and secondly of coral reefs. Reef facies types are mostly reef core facies and back reef lagoon facies. Minerals in reef rocks are simplex, mainly consist of carbonate, involving low-magnesian calcite and ferroan dolomite. Textural components are organism framework, granular fragment, micrite and calcsparite. Rock types comprise framework limestone/dolostone, boundstone, grain limestone/dolostone, with organic framework texture, biology baffle texture, geniculum texture, binding texture, and cementitious texture. Reservoir pore space types are primary pore including intergranular pore and visceral foramen, and secondary pore including moldic pore, fissure, intragranular emposieu, enlarged intergranular pore, which mostly exists as intergranular pore-emposieu-intercrystal pore, with good storage capability.
A high-resolution, two-dimensional seismic survey covering 7500 km 2 provides an unprecedented view of the evolution of a Miocene-Pliocene carbonate platform in the East Natuna-Sarawak Sea, Indonesia. The Segitiga Platform (1400 km 2) contains Terumbu Formation carbonate strata as much as 1800 m thick that were deposited in platform interior, reef and shoal margin, and slope to basin environments. The Segitiga Platform was subdivided into 12 seismic sequences that demonstrate a history of (1) initial isolation, (2) progradation and coalescence, (3) backstepping and shrinkage, and (4) terminal drowning. Interpretations of seismic facies maps for each sequence were used to help illustrate platform history. These seismic fades maps indicate that the Segitiga Platform originated as three smaller platforms on extensional fault-block highs. Deep intraplatform seaways separated these smaller platforms. Progradation of shallow-water carbonates filled the seaways during a phase of coalescence and the three platforms were amalgamated to form a merged composite platform (1400 km2; middle-upper Miocene). A rapid relative rise in sea level at the end of Miocene time caused a major backstepping of the carbonate margins (and a concomitant drowning of the adjacent Natuna field carbonate platform to the east) resulting in a platform of greatly reduced size (600 km 2) during the lower Pliocene. Rapid subsidence, combined with an eustatic rise at the end of the early Pliocene, caused terminal drowning of the Segitiga Platform. The platform was buried by younger siliciclastics of the Muda Formation. Eustatic sea level change controlled the timing of sequence-boundary formation, but structural movements modified internal sequence character and fades distribution. Faulting created topography that acted as templates for the initiation of carbonate platform deposition and provided pedestals for the localization of backstepped platforms. Cessation of faulting may have instigated progradation of the platform resulting from the deceleration of accommodation-space production. Regional subsidence may have controlled the location and extent of platform backstepping. Geographic variability in sequence stacking of coeval platform margins is observed over relatively short distances. Progradation is most strongly developed on the leeward side of the platform, but increased accommodation resulting from the rapid local subsidence or changing oceanographic currents also influenced the direction and magnitude of progradation.
In this study, the Miocene carbonate sequence stratigraphy and sedimentary cycle of Nankang platform and L-structure in Zengmu basin are analyzed by using drilling, seismic and some palaeontologic data, and the sequence pattern of Miocene carbonate in the study area is established. The results show that three large-scale carbonate sedimentary cycles occurred during Mid to Late Miocene (5.3-16 Ma) in Zengmu basin, so the strata can be subdivided into three Tertiary sequences (SQ1, SQ2 and SQ3 sequences). SQ1 and SQ3 sequences are defined as the classical type I carbonate sequences, which are composed of dense algal limestone in low-stand system tracts (LST), argillaceous limestone in transgressive system tracts (TST) and coral limestone in high-stand system tracts (HST). And their properties indicate that the carbonate buildups have experienced a process from open marine platform facies to reef flat facies. Being different form SQ1 and SQ3 sequences, SQ2 sequences belong to the drowned unconformity type of carbonate sequences. This kind of carbonate sequences is marked by the successions consisted of argillaceous limestone of condensed sequence (CS) and coral limestone (or clastic limestone) of HST. And its development generally occurred during the phase of continuous decrease of sea level.
Lithologic variations and sequence stratigraphy in large basins (or basin groups) demonstrate the impacts by changes in depositional environments and reflect the stepwise evolution of the China Seas. Nonmarine deposits are prevalent in basins now lying in shallow water depths. Marine deposition increases in postrift sequence and particularly the deepwater sectors of basins. Deep-sea isotopic and astronomical stratigraphy mainly from ODP Leg 184 results is summarized to provide examples of new stratigraphic controls.
The Mega Platform is a 30- × 50-km-large and 1.2-km-thick middle Miocene carbonate platform located in the Luconia Province, offshore Sarawak, Borneo. The platform originated in the late early to early middle Miocene on a regional fault-bounded structural high, first aggraded and then backstepped during a series of third-order sea level fluctuations during the middle Miocene (TB2.3-2.6). The Jintan Platform termination with an area of 8 × 12 km is one of the prominent backsteps toward the top of the Mega Platform. Three-dimensional (3-D) seismic indicates that growth on Jintan ceased relatively early with continued carbonate aggradation in adjacent smaller terminations (M1, M1-East). Spectacular reservoir architecture and diagenesis are revealed by the seismic. Several transgressive, aggradational, and progradational cycles are overprinted by repeated karst events. Dissolution features and bank-margin collapse are aligned to a deep-seated regional fault system, which periodically became reactivated during carbonate growth. A large triangular-shaped graben formed during one of the faulting periods but subsequently healed by a prograding reefmargin sequences. Two alternative scenarios are presented to explain the ultimate demise of the platform. The first proposes drowning resulting from a combination of subsidence and eustatic sea level rise. The second evokes a much-later drowning, which was preceded by a long period of exposure resulting from a second-order sea level fall and an initial decrease in subsidence caused by the onset of tectonism in Borneo during the late Miocene. In any case, following a hiatus of about 5 m.y., the platform was finally buried by deep-marine siliciclastics that prograded into the basin from the large delta systems of northwest Borneo. Recognition of growth architecture, faulting, and karstification is a key to exploiting the hydrocarbon reservoirs of the Mega Platform. A 30-m-thick low-porosity and -permeability layer shields the gas trapped in Jintan from the underlying aquifer. Penetrated by only one well, the extent of the layer and areas of breaching caused by faulting and karstification are identified on seismic. Interpretation of the seismic is critical to assessing whether and how the underlying aquifer is felt during reservoir depletion and whether there is pressure communication between adjacent reservoirs connected via the aquifer. Cores and logs from three wells provide ground truthing of reservoir architecture, karst features, and faulting derived from the interpretation of reflection and inversion seismic. The interpretation is then imported into static and dynamic 3-D models to constrain reservoir properties, predict dynamic behavior, and guide optimum field development.
Based on a large quantity of seismic data interpretation and some drilling data in Wan'an basin, the Miocene Wan'an carbonate platforms are identified from seismic reflection profiles and their sedimentary characteristics as well as spatial and temporal distributions are documented in detail. The Wan'an carbonate platforms developed initially during the Early Miocene and reached its prosperous period during the Middle Miocene, showing north-south orientation, and mainly occurring on the hanging wall of the strike-slip fault block in the centre of the basin and the southern basin margin. The Miocene Wan'an carbonate platform can be divided into the east band and the west band according to two different sedimentary tectonic forming backgrounds, where the west side is the slope dipping towards the east fractured by faults and approaches land-source areas resulting in alternating clastic and carbonate rocks, while the east side is close to the South China Sea basin and far from terrigenous areas showing thick and pure carbonate rocks. The sequence stratigraphic analyses show that the Wan'an carbonate platform exists mainly in transgressive and highstand system tracts. The sedimentary facies of single carbonate platform show ring construction in the plane view, and they are relatively narrow but regular, which may be divided into inner platform facies, fringing platform facies, foreslope facies (ramp and steep slope) and basin floor facies. However, the basin floor facies are found only in the eastern side of carbonate platform which may be related to the geological settings near the South China Sea.
It is known from macrocomparisons and microresearches of bioherm reservoirs in main sedimentary basins of the South China Sea through deep-water petroleum explorations and by means of 2D/3D seismic data and a whole-coring core from the Xisha (西沙) Islands that there are great differences between deep-sea oil and gas fields in the world and those in the South China Sea, as reservoir systems of the former are mainly clastic rocks, whereas the latter have organic reefs that act as reservoirs of their largest oil and gas fields, which are represented by large Liuhua (流花) 11-1 reef oilfield in the north and super-large L reef gas field in the south of the South China Sea. Therefore, it is of great significance to study deep-water bioherm reservoirs in the South China Sea. Comparisons of organic reefs in the four large islands of the South China Sea give evidences that such reefs in main sedimentary basins came into being during Cenozoic, especially in Neogene, and mainly occur as tower (point) reef, massive reef, platform-edge reef, and patch reef in shape, which show different reservoir physical properties and seismic reflection configurations and make up carbonate rock-bioherm formations in the island reef and sedimentary basin areas. Generally, the south and north parts differ from the east and the west of the South China Sea in geologic conditions, as their corresponding continental shelf/island shelf areas are relatively wide/narrow, large stream current systems are well developed/not so well developed, and terrigenous sediments are relatively sufficient/insufficient. The southeast and south parts of the South China Sea had organic reefs built up earlier than the north and the reef building mainly took place in Neogene; these Neogene organic reefs all belong to plant algal reef rocks. Liuhua oilfield in the Pearl River Mouth basin is found to mainly have red algal bindstone, Malampaya reef in the northern Palawan basin is rich in both red algal bindstone and green algal reef segmented rock, and especially Miocene red algal framestone and green algal segmented rock are discovered in the Xisha Islands. These algal reefs created different sedimentary microfacies as well as various rock structures and types, and through recent researches on the mechanism of dolomitization, freshwater dolomite was discovered and grouped under products from dolomitization in mixed water that was regression reefal dolomite of good reservoir properties.
This chapter addresses the use of seismic data, particularly where they are correlated with well information, to identify and interpret the carbonate depositional systems associated with three major types of carbonate play. These plays can be ranked in order of decreasing size as: (1) carbonate sheets, (2) carbonate buildups, and (3) clinoform carbonate shelf margins. Sheet plays are found in carbonate shelf sediments associated with the shallow water behind the basin margin; buildup plays occurs down-slope from the margin and on the shallow shelf immediately adjacent to the margin; clinoform plays are associated with the margin crest. The depositional porosity and geometry of these plays may be modified by subsequent fracturing and diagenesis. Seismic interpretations of these plays can be tested with computer simulations which model the fill of sedimentary basins. The input parameters to such simulations are assumptions about the processes of sedimentation, sea level history, and tectonic evolution of the study area. The parameters are based on currently accepted sedimentological, tectonic, and eustatic models.
Carbonates in SE Asia range in age from Palaeozoic to Recent, but are most important as reservoirs in the Neogene where they comprise a major target for hydrocarbon exploration (e.g. Batu Raja Formation, South Sumatra, Sunda and Northwest Java basins). Carbonates of pre-Tertiary, Palaeogene and Neogene age all show a strong diagenetic overprint in which dolomite occurs as both cementing and replacive phases associated with variable reservoir quality. This paper reviews published data on the occurrence and types of dolomites in SE Asian carbonates, and considers the models that have been used to explain the distribution and origin of dolomite within these rocks.
Pre-Tertiary carbonates form part of the economic basement, and are little studied and poorly understood. Although some, such as in the Manusela Formation of Seram, may form possible hydrocarbon reservoirs, most are not considered to form economic prospects. They are best known from the platform carbonates of the Ratburi and Saraburi groups. in Thailand, and the oolitic grainstones of the Manusela Formation of Seram. The Ratburi Group shows extensive dolomitization with dolomite developed as an early replacive phase and as a late-stage cement.
Palaeogene carbonates are widely developed in the region and are most commonly developed as extensive foraminifera-dominated carbonate shelfal systems around the margins of Sundaland (e.g. Tampur Formation, North Sumatra Basin and Tonasa Formation, Sulawesi) and the northern margins of Australia and the Birds Head microcontinent (e.g. Faumai Formation, Salawati Basin). Locally, carbonates of this age may form hydrocarbon reservoirs. Dolomite is variably recorded in these carbonates and the Tampur Formation, for example, contains extensive xenotopic dolomite.
Neogene carbonates (e.g. Peutu Formation, North Sumatra) are commonly areally restricted, reef-dominated and developed in mixed carbonate-siliciclastic systems. They most typically show a strong diagenetic overprint with leaching, recrystallization, cementation and dolomitization all widespread. Hydrocarbon reservoirs are highly productive and common in carbonates of this age. Dolomite is variably distributed and its occurrence has been related to facies, karstification, proximity to carbonate margins and faults. The distribution and origin of the dolomite has been attributed to mixing-zone dolomitization (commonly in association with karstic processes), sulphate reduction via organic matter oxidation, and dewatering from the marine mudstones that commonly envelop the carbonate build-up.
Dolomite has a variable association with reservoir quality in the region, and when developed as a replacive phase tends to be associated with improved porosity and permeability characteristics. This is particularly the case where it is developed as an early fabric-retentive phase. Cementing dolomite is detrimental to reservoir quality, although the extent of this degradation generally reflects the abundance and distribution of this dolomite.
Dolomitization is also inferred to have influenced the distribution of non-hydrocarbon gases. This is best documented in North Sumatra where carbon dioxide occurs in quantities ranging from 0 to 85%. There are a number of possible mechanisms for generating this CO 2 (e.g. mantle degassing), although the most likely source is considered to be the widely dolomitized Eocene Tampur Formation that forms effective basement for much of the basin. High heat flows are suggested to have resulted in the thermogenic decomposition of dolomite with CO 2 produced as a by-product.
The Zengmu Basin is a large Tertiary marine sedimentary basin in the southern region of the South China Sea. It is considered to have multiple combinations of source rocks, reservoirs and caprock, making it a favourable prospect for oil and gas. Seismic investigations have shown that this has three tectonic sequences separated by two unconformities. The upper sequence consists of Oligocene to Recent marine sediments, the middle sequence is thought to be composed of Paleogene to Eocene shelf, neritic clastic deposits and the lower sequence is interpreted as being pre-Tertiary metamorphic or igneous rocks.The development of the basin has been controlled by faults, especially by northwest-trending faults, leading to gradual stepped-block subsidence to the northeast. Three fault systems trending NW, NE and S-N separate the basin into ten secondary tectonic units with five depressions and five highs. Taking into account the seismic reflection data collected during the 1987 survey by the Shiyan II and the geological information available from earlier work, this paper elucidates our understanding of the sequences division, and tectonic subdivision, and of the formation, evolution, and oil and gas prospects of the Zengmu Basin.
Cenozoic equatorial carbonate production was at its most extensive and diverse in the seas of Southeast Asia, yet the carbonates of this region remain poorly documented. This paper presents the first published review of carbonate deposition during the Cenozoic, collating sedimentological data for carbonate successions throughout the region. Current models of warm-water carbonate platform evolution, sedimentation and facies distribution, inspired by studies of the classic (sub)tropical areas, provide inadequate analogues for the evaluation of modern or Cenozoic equatorial carbonates in Southeast Asia. The equatorial carbonates differ in being dominated by bioclasts. Coated grains and associations with evaporites or dolomites are rare. The carbonate systems occur in a range of depositional settings which were often affected by coeval tectonism, siliciclastic input or volcanism. An understanding of the carbonate depositional environments, spatial facies distributions and controls on deposition and diagenesis is essential in order to characterize equatorial carbonate development and to evaluate their considerable economic potential.
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